In the run-up to the 2016 Holyrood election, the SNP had pledged not to increase the basic rate of the levy during the whole five years of the parliamentary term.

But it is now widely expected Finance Secretary Derek Mackay will use December’s Scottish Budget to bring in an income tax hike, after First Minister Nicola Sturgeon signalled it was time for a discussion on the “responsible and progressive” use of Holyrood’s tax powers.

Former finance secretary John Swinney - who was standing in for Ms Sturgeon at First Minister’s Questions today after she was involved in climate change talks in Germany - said the Scottish Government would have to make some “real hard decisions”.

And despite speculation that income tax is about to rise, the Deputy First Minister said the SNP would “stand shoulder-to-shoulder with low income households in Scotland and take the right decisions to protect their incomes”.

Mr Swinney hit back after coming under sustained attack from the Scottish Conservative leader on the issue.

Ms Davidson said: “The truth is the SNP wheeled out Mr Swinney, ‘honest John’, before the election to tell people that their taxes wouldn’t go up, and as soon as they got back in those promises turned to dust.”

She said that before the Scottish elections in May 2016 Mr Swinney had said a “tax rise would be a punishment” for low income workers.

She challenged Mr Swinney and said: “Can the Deputy First Minister explain why the SNP said one thing to people about taxes when they needed their votes, and another once they had them?”

This year has been the first that Holyrood has had power over income tax rates and bands, but in 2017-18 ministers opted to make minor changes, keeping the threshold for the 40p rate of tax at £43,000 instead of copying Westminster’s example and increasing it to £45,000.

Scottish Tories opposed this move at the time, arguing it would make Scotland the “highest taxed part of the UK”.

With the Scottish Budget, including the government’s tax plans for 2018-19, due to be revealed next month, the issue is once again high on the political agenda.

Ms Davidson recalled that in April 2016, a month before the Holyrood vote, Mr Swinney had “promised that basic rate taxpayers would not see their tax bills rise” - saying at the time he had described this as “the right reassurance to give people who are already finding it challenging to make ends meet”.

He also pledged to voters then that they had this “reassurance for the remainder of the parliamentary term”.

But now the Conservative leader said: “It sounds to me like the Deputy First Minister isn’t prepared to stick to that promise.”

Continuing her attack, she added: “Just a few weeks before the election he said this: ‘I want to say to teachers and public service workers the length and breadth of the country, I value the sacrifices they have made and the last thing I am going to do is put up their taxes’.

“The last thing? It turns out the only thing you lot are going to do with taxes is put them up.”

She then accused the SNP of saying “one thing before an election, the exact opposite after” as she asked Mr Swinney if this was “honest government”.

Mr Swinney said: “The Scottish Government is engaged in a substantive debate with members of the public about the real choices that are faced when you are in government, when you are trying to address the fact that public expenditure has been slashed by the United Kingdom government and that austerity continues to roll forward year by year.

“So we are involved in that discussion because we have to take the real hard decisions in government.”

He also stressed the SNP would “act at all times to protect the interests of low income individuals within our society”.

Mr Swinney also highlighted times when Scottish ministers had used part of their funding to mitigate welfare changes brought in by Westminster.

“When the United Kingdom government slashed council tax benefit, this Scottish Government came to the rescue, this former finance secretary came to the rescue of low income families within Scotland,” he insisted.

“When the bedroom tax was applied by the Conservative government, this former finance secretary came to the rescue of low income households in Scotland.

“So I am absolutely determined to make sure we stand shoulder-to-shoulder with low income households in Scotland and take the right decisions to protect their incomes.”

The Deputy First Minister stated: “The government is engaged in discussing with members of the public about the correct stance to take on taxation to make sure we can fund effectively the public services of Scotland to meet the needs of the people of our country and to invest in developing the Scottish economy given the significant economic challenges we face arising out of Brexit.

“Those are the issues the government will discuss as part of the consultation with members of the public, that is the right approach to take forward and the Finance Secretary will announce the conclusions of that in the budget in December.”